A search will be conducted for conditional yeast mutants deficient in the synthesis and regulation of important membrane lipids. These mutants will be characterized both genetically and biochemically. Rates and timing of synthesis of individual lipids, during meiosis and the mitotic cell cycle will be determined in both wild type and mutant yeast. The dependence of basic cellular processes such as macromolecular synthesis, nuclear division and chromosome separation on lipid biosynthesis will be assessed and roles of individual lipids studied. Since lipids are important components of biomembranes, it is hoped that the information gained will give some insight into the timing and control of membrane biosynthesis during cell division and into the structural and functional roles of lipids in membranes. Very little is presently known about the molecular organization of biological membranes or about membrane synthesis. Because membranes are involved in a multiplicity of cellular processes including the transport of substances into and out of cells, they must be expected to play an important part in both normal and abnormal cell growth and differentiation. Indeed, alterations in cell membranes are characteristic of some mammalian neoplastic tissues (9). The information gained from the study of membrane components in a model eukaryote such as yeast may, therefore, contribute to an understanding of the involvement of biomembranes in both normal and abnormal differentiation such as that leading to oncogenesis.